4,320 research outputs found
Weibel instability and associated strong fields in a fully 3D simulation of a relativistic shock
Plasma instabilities (e.g., Buneman, Weibel and other two-stream
instabilities) excited in collisionless shocks are responsible for particle
(electron, positron, and ion) acceleration. Using a new 3-D relativistic
particle-in-cell code, we have investigated the particle acceleration and shock
structure associated with an unmagnetized relativistic electron-positron jet
propagating into an unmagnetized electron-positron plasma. The simulation has
been performed using a long simulation system in order to study the nonlinear
stages of the Weibel instability, the particle acceleration mechanism, and the
shock structure. Cold jet electrons are thermalized and slowed while the
ambient electrons are swept up to create a partially developed hydrodynamic
(HD) like shock structure. In the leading shock, electron density increases by
a factor of 3.5 in the simulation frame. Strong electromagnetic fields are
generated in the trailing shock and provide an emission site. We discuss the
possible implication of our simulation results within the AGN and GRB context.Comment: 4 pages, 3 figures, ApJ Letters, in pres
Renormalized parameters and perturbation theory for an n-channel Anderson model with Hund's rule coupling: Asymmetric case
We explore the predictions of the renormalized perturbation theory for an
n-channel Anderson model, both with and without Hund's rule coupling, in the
regime away from particle-hole symmetry. For the model with n=2 we deduce the
renormalized parameters from numerical renormalization group calculations, and
plot them as a function of the occupation at the impurity site, nd. From these
we deduce the spin, orbital and charge susceptibilities, Wilson ratios and
quasiparticle density of states at T=0, in the different parameter regimes,
which gives a comprehensive overview of the low energy behavior of the model.
We compare the difference in Kondo behaviors at the points where nd=1 and nd=2.
One unexpected feature of the results is the suppression of the charge
susceptibility in the strong correlation regime over the occupation number
range 1 <nd <3.Comment: 9 pages, 17 figure
Particle Acceleration, Magnetic Field Generation, and Associated Emission in Collisionless Relativistic Jets
Nonthermal radiation observed from astrophysical systems containing
relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray
bursts (GRBs), and Galactic microquasar systems usually have power-law emission
spectra. Recent PIC simulations using injected relativistic electron-ion
(electro-positron) jets show that acceleration occurs within the downstream
jet. Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas.
Plasma waves and their associated instabilities (e.g., the Buneman instability,
other two-streaming instability, and the Weibel instability) created in the
shocks are responsible for particle (electron, positron, and ion) acceleration.
The simulation results show that the Weibel instability is responsible for
generating and amplifying highly nonuniform, small-scale magnetic fields. These
magnetic fields contribute to the electron's transverse deflection behind the
jet head. The ``jitter'' radiation from deflected electrons has different
properties than synchrotron radiation which assumes a uniform magnetic field.
This jitter radiation may be important to understanding the complex time
evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and
supernova remnants.Comment: 4 pages, 3 figures, contributed talk at the workshop: High Energy
Phenomena in Relativistic Outflows (HEPRO), Dublin, 24-28 September 2007.
Fig. 3 is replaced by the correct versio
GRB spectral parameters within the fireball model
Fireball model of the GRBs predicts generation of numerous internal shocks,
which then efficiently accelerate charged particles and generate magnetic and
electric fields. These fields are produced in the form of relatively
small-scale stochastic ensembles of waves, thus, the accelerated particles
diffuse in space due to interaction with the random waves and so emit so called
Diffusive Synchrotron Radiation (DSR) in contrast to standard synchrotron
radiation they would produce in a large-scale regular magnetic fields. In this
paper we present first results of comprehensive modeling of the GRB spectral
parameters within the fireball/internal shock concept. We have found that the
non-perturbative DSR emission mechanism in a strong random magnetic field is
consistent with observed distributions of the Band parameters and also with
cross-correlations between them; this analysis allowed to restrict GRB physical
parameters from the requirement of consistency between the model and observed
distributions.Comment: 14 pages, 17 figures, MNRAS in pres
Landau damping of partially incoherent Langmuir waves
It is shown that partial incoherence, in the form of stochastic phase noise,
of a Langmuir wave in an unmagnetized plasma gives rise to a Landau-type
damping. Starting from the Zakharov equations, which describe the nonlinear
interaction between Langmuir and ion-acoustic waves, a kinetic equation is
derived for the plasmons by introducing the Wigner-Moyal transform of the
complex Langmuir wave field. This equation is then used to analyze the
stability properties of small perturbations on a stationary solution consisting
of a constant amplitude wave with stochastic phase noise. The concomitant
dispersion relation exhibits the phenomenon of Landau-like damping. However,
this damping differs from the classical Landau damping in which a Langmuir
wave, interacting with the plasma electrons, loses energy. In the present
process, the damping is non-dissipative and is caused by the resonant
interaction between an instantaneously-produced disturbance, due to the
parametric interactions, and a partially incoherent Langmuir wave, which can be
considered as a quasi-particle composed of an ensemble of partially incoherent
plasmons.Comment: 12 page
Magnetic-field dependence of antiferromagnetic structure in CeRh1-xCoxIn5
We investigated effects of magnetic field H on antiferromagnetic (AF)
structures in CeRh_{1-x}Co_xIn_5 by performing the elastic neutron scattering
measurements. By applying H along the [1,-1,0] direction, the incommensurate AF
state with the propagation vector of q_{h1}=(1/2,1/2,0.297) observed at H=0 is
replaced by the commensurate AF state with the q_{c2} = (1/2, 1/2, 1/4)
modulation above 2 T for x=0.23, while the AF states with the
q_{c1}=(1/2,1/2,1/2) and q_{h2}=(1/2,1/2,0.42) modulations seen at H=0 change
into a single q_{c1}-AF state above ~1.6 T for x=0.7. These results suggest the
different types of AF correlation for Co concentrations of 0.23 and 0.7 in an
applied magnetic field H.Comment: 4 pages, 2 figures, to appear in the proceedings of ICM2009
(Karlsruhe, Germany
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